This invention relates to ink jet apparatus for ejection of ink droplets, and more particularly, to an ink jet apparatus having a normally vented reservoir with a non-spill configuration.
The use of hot melt ink in ink jet systems, which ink is normally in a solid or frozen state but attains a liquid state or phase when its temperature is raised, has presented a number of advantages to ink jet apparatus. For a discussion of the characteristics of such ink and use thereof in ink jet apparatus, reference is made to U.S. Pat. No. 4,390,369 and pending U.S. patent applications Ser. No. 610,627 filed May 16, 1984, Ser. No. 565,124 filed Dec. 23, 1983, and Ser. No. 644,542 filed Aug. 27, 1984, all assigned to the same assignee as this invention and incorporated herein by reference.
While the use of hot melt ink has presented advantages as discussed in the above references, it also creates additional requirements for the design of the apparatus in which it is used. Since the ink supply is replenished by dropping or injection of pellets into the apparatus, the reservoir needs to have a normally open port through which the ink enters when it is first received and melted. Although the apparatus may be capped with a cover or lid in order to protect the reservoir from infusion of dirt or other contaminants, it is difficult to achieve a leak proof reservoir housing which can prevent leaking or spillage when tilted or jarred by external forces. The apparatus must allow ready access for the addition of the solid ink pellets, with the result that it is difficult to provide the required integrity against spilling or leaking of liquid ink from the reservoir.
A loss of ink due to spillage or leaking is a severe problem for any ink jet apparatus, since voiding the ink jet head of ink can result in rendering the apparatus totally inoperable. This is normally not a severe problem in ink jet apparatus employing standard single phase liquid ink, since conventional arrangements provide for sealing of the ink within the apparatus. However, these conventional sealing arrangements are not applicable to the hot melt ink application where replenishment is accomplished by insertion of a pellet or pellets of ink into the apparatus, followed by heating of the pellet to transform it to the liquid phase.